For energy saving reasons, it is often convenient, when a computer is not in use, that it is either: powered down; or placed in a very low power consumption state. For some applications, entirely powering down a computer is not acceptable. For example, a computer connected to a network cannot be managed from a remote site if the computer is entirely powered down.
One alternative is to have a subsystem of the computer maintained at full power for the reception of packets from the network, so that a special computer on the network may issue a special "wake-up" packet, the reception of which causes the computer to become powered up. However, a disadvantage of the use of a special computer transmitting a special "wake-up" packet is that the special computer may have a list of many computers on the network which it must awaken. Maintaining such a list, updating the list, and awakening computers on the network is a clumsy and undesirable solution to the dual problem of both remote management of networked computers, and of maintaining the computers in a low power mode, or "asleep", and then awakening the computer.
There is needed a reliable and simple means to awaken a computer which is substantially powered down and which is connected to a network, and not having to maintain a special computer to awaken sleeping computers by transmission of special "wake-up" packets on the network.